1. Field of the Invention
The present invention relates generally to a display device. More specifically, the invention relates to a display control device controlling brightness of display of various display equipments installed in a vehicular cabin.
2. Description of the Related Art
FIG. 7 is a block diagram of a mobile phone installed within a vehicular cabin as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 56-71343. In FIG. 7 a brightness control line 10 is connected to a vehicular battery (not shown) via a lighting switch (not shown). When the lighting switch is turned ON, a battery voltage is applied to the brightness control line 10.
A microcomputer 8 is responsive to the battery voltage applied to the brightness control line 10 to control display of a display arrangement 9 via a display device drive circuit, and, in conjunction therewith, to perform lighting control for an illumination lamp 12 via a lamp driver circuit 13.
While the lighting switch is held OFF, the battery voltage is not applied to the brightness control line 10 and therefore, the display brightness of the display arrangement 9 is not controlled. Also, lighting control for the illumination lamp 12 is not performed.
In such conventional display equipments to be installed in the vehicular cabin, there is provided a manually operable dimmer circuit for controlling lighting intensity of the display arrangement, illumination lamp and further a back-light for display in association with the vehicular lighting switch or an automatic dimmer circuit for automatically controlling lighting intensity of the display arrangement or the back-light with taking a predetermined light intensity level as a threshold value.
In such conventional display control system, it has been difficult to assure good visibility in a wide brightness range from direct insolation of the sun beam to the dark. Also, the brightness control of the display equipment cannot satisfactorily follow the adaption of human pupil to abrupt variation of the light intensity at the entrance and exit of a tunnel.